Control gear for ship stabilisation



Fe 2, 1 J. BELL 2,923,874

CONTROL GEAR FOR SHIP STABILISATION Filed Dec. 17, 1956 United States Patent 2 23 14 coNTRoL GEAR FOR SHIP STABILISATION John Bell, Beckenham, England, assignor to Muirhead & Co. Limited, Beckenham, England Application December 17, 1956, Serial No. 628,654

Claims priority, application Great Britain December 22, 1955 5 Claims. (Cl. 318-489) This invention relates to control gearfor ship stabilization systems and more particularly to systems intended for stabilization against roll.

Various methods are known to provide stabilization against roll, such as moving weights which are transferred. from one side of the ship to the other, similar systems in which water is used instead of the moving weight, water jets of high power and activated fins. The invention may be applied to any of these systems since. it resides in the sensing means which direct the stabilizing means. For the sake of clarity, the invention will be described with particular reference to an activated fin system.

In activated fin systems one or more fins or hydroplanes project from each side of the ship, mounted on shafts so that they may be rotated through a certain angle on either side of a central, neutral position in which they exert no torque upon the ship. When the ship rolls, the fins on either side of the ship are tilted in opposite directions and by virtue of the ships movementthrough the water they impose a torque upon the ship which opposes the undesired roll.

The control gear comprises sensing means which detect or measure one or more functions of the roll and provide a signal which may be in electrical or mechanical form. This in turn directs control gear having sufl'icient power to operate the stabilizing means. It is usual to employ vertical-keeping and velocity-sensitive or rate gyroscopes of well known type as the sensing means. The vertical keeping gyroscope is usually provided with erecting means which ensure that its axis remains truly vertical. The relative angle between the structure of the shap and the gyroscope axis is thus a measure of the departure of the ship from the vertical position. The velocity-sensitive gyroscope is employed to measure the velocity of the roll. Further functions of the roll such as acceleration or higher time derivatives may also be determined. Signals corresponding to one or more of these functions are combined in any desired manner and a signal which is related to the instantaneous characteristic of the roll is applied to the control gear.

Due to various factors which may be of a permanent or temporary nature, the ship may tend to remain slightly out of the vertical position. Bad stowage of cargo or stores may alter the ships trim for the duration of the voyage or its trim may change slowly as fuel is consumed. More temporary factors, such as a steady wind or continuous helm applied to keep the ship travelling in the desired direction relative to a cross current may cause the ship to heel or list to one side for a more or less lengthy period. In any of these cases, the vertical keeping gyroscope will deliver a steady signal corresponding to the heel of the ship in the absence of roll and when roll is present the signal will depend both upon the roll and the heel. In consequence, the stabilizing gear will endeavour to stabilize against roll and also continuously to push the ship into an upright position.

The major portion of the energy used to stabilize the ship is derived from the ships engines since the fins exert a drag on the ship corresponding to the stabilizing torque which they develop; thus since some of the propulsive energy is diverted to the stabilizers, the ships speed is reduced by a small but definite amount. In cases where correction of heel is not required the stabilizing gear exerts an unnecessary drag on the ship in the attempt to push the ship into its upright position and, furthermore, the amount of stabilizing effort available for the intended purpose of stabilization against roll may be reduced to a serious extent.

The invention consists of an apparatus for inclusion in a control gear for ship stabilization which, for the purpose of description, may be of the known type embodying a vertical-keeping gyroscope responsive to roll angle and a velocity-sensitive gyroscope responsive to the velocity of the roll, signals from which are combined to produce a third signal for activating the stabilizing means. The aforesaid apparatus is associated with the verticalkeeping gyroscope and has for its purpose the generation of a signal proportional to the angle of heel of the ship. The apparatus according to the invention comprises a control member controlled by the vertical-keeping gyroscope and attached to set itself to a mean position between the limits of the excursions of the gyroscope due to the roll. The control member moves very slowly so that it eventually sets itself to the angle of heel over a relatively long period, for example, several minutes, and is substantially unaffected by the roll or by quick heeling movements due, for example, to gusts of wind, such quick movements being treated by the invention as part of the roll. A signal derived from the control member is employed to bias or modify the signal derived from the vertical-keeping gyroscope so that the modified signal corresponds to the roll of the ship in relation to the angle of heel.

The invention Will now be described in conjunction with the accompanying drawings in which:

Figure 1 shows schematically the complete ship stabilizing gear including the subject of the invention.

Figure 2 shows an alternative arrangement of part of Figure 1.

It is to be clearly understood that these embodiments are given only by way of example and that many variations of the practical form of the invention are possible by substituting other electrical, electromagnetic, mechanical or hydraulic equivalents for the elements shown.

In the vertical-keeping gyroscope 1, in Figure l, the wheel rotates about the vertical dotted axis 2 and the casing is pivoted about axis 3, set at right-angles to axis 2, so that axis 2 is enabled to remain truly vertical despite the roll or heel of the ship. The movement of gyroscope 1 about axis 3 relative to the ship is transmitted by lever 4, link 5 and lever 6 to the rotor of synchro or magslip transmitter 7. The same gyroscope movement is also transmitted through link 8 to contact arm 9 which is pivoted at 10. A control member in the form of a sector plate 11 is also pivoted at 10 and has two contact sectors 12 and 13 insulated from the sector plate and from each other. Contact arm 9 is connected to an alternating current supply, the other pole of this supply being connected through capacitor 14 to the centre of the winding 15 of a known type of two-phase induction motor 17 having windings 15 (centre tapped in this instance) and 16 and rotor 17a. Winding 16 is connectcdv to the same alternating supply as arm 9. Assuming that the ships trim is truly vertical and that there is no roll, then lever 4 is vertical and arm 9 is also vertical. If, now, the ship rolls, gyroscope 2 remains in its upright pOsition, lever 4 in effect begins to oscillate in relation to the ship structure and its oscillation is. ttansmitted,

through link 5 and lever 6 to the rotor of synchro unit normally having a single winding on its rotor which,:

in the case of a transmitter, is connected to an alternat ing current supply. The stator has three equally spaced windings similar to those of a three-phase induction motor. The alternating magnetic field set up by the rotor induces voltages in the three stator windings which vary in relation to each other according to the angular position of the rotor. Thus three voltages appear between stator output connections 19 and may be resolved by a. similar synchro used as a receiver into an electrical signal or a mechanical angular position corresponding'to the angular position of the rotor of synchro transmitter 7.

In this way the oscillations of lever 4 may be transmitted by three lines connected to output leads 19 to a distant point.

For the purpose of the present invention, synchro 7 has a second rotor winding, at right-angles to the normal energizing winding, brought out to connections 22 (one of which is generally common to the energizing winding) which will be referred to later.

The movement of lever 4 is also transmitted by link'8 to contact arm9 causing contact 18 attached to arm 9 to connect control winding 15 to the alternating current supply in one sense or the other, depending upon whether sector 12 or sector 13 is connected. Thus the rotor 17a of the two-phase motor will rotate in one direction when sector 12 is connected and in the opposite direction when sector 13 is connected. Rotor 17a rotates a sector plate 11 through a high-ratio reduction gear so that sector plate 11 rotatesat a rate of, say, one degree per minute. The rotation of sector plate 11 is communicated to the rotor of induction regulator 20 by means of gear teeth on sector plate 11 and gear 21 attached to the rotor of induction regulator 20.

The rotor of induction regulator 20 is energized from the alternating current supply and the output from its stator at terminals 23 is connected to the cross winding on the rotor of synchro 7 at terminals 22.

The rotation of rotor 17a is arranged so that if contact 18 is connected to sector 12, then sector plate 11 is rotated to move sector 12 away from the central position and rotation of sector plate 11 is in the opposite sense when sector 13 is connected. If the ship is correctly trimmed and there are no other factors to cause a temporary heel, then the excursions of lever 4 on either side of axis 2 in response to roll are approximately equal so that sector plate 11 oscillates about the central position but, because of the high gear reduction ratio, its oscillations are extremely small and the output voltage of induction regulator 20 is negligible.

If, for any reason, the ship heels, then the excursion of lever 4 on one side of true vertical axis 2 is greater than its excursion on the other side, and rotor 17a runs for a longer period in one direction than it does in the other direction so that, over a number of roll cycles, sector plate 11 is gradually displaced to one side or other of its normal centre. Eventually it reaches a position corresponding to the angle of heel and the voltage delivered by induction regulator 20 corresponds. This corresponding to the new angle of heel. In the velocity sensitive or rate gyroscope 34 the wheel rotates about axis 35 which is horizontal and athwartships and the casing 36 is pivoted about the vertical axis 37. Movement of the casing about the vertical axis is centralized by springs 38. Rolling motion of the ship causes corresponding gyroscopic precessional forces and, as is well known, these forces acting against the centralizing springs result in movement of the casing about the vertical axis which is proportional to the instantaneous velocity of the roll. Casing 36 is rotationally coupled to the rotor of synchro transmitter 39, the stator of which produces a signal proportional to roll velocity, this signal is received by the winding stator of differential synchro 40 and the aforesaid combined signal over lead 19 from the stator of synchro transmitter 7 is supplied to the three winding rotor of the diiferential synchro 46 The resultant mechanical output from the rotor of differential synchro 40 controls the actuating means 41 for the fin 42; consequently the stabilizing gear acts to stabilize the ship to the angle of heel and not the true vertical position.

It will be understood that the three alternating current supplies shown may be the same or may be of different voltages to suit the requirements of the elements to which they are connected, but they must be substantially in phase with each other.

Figure 2 shows an alternative embodiment of the invention which produces the same efiect but does not require contacts for the operation of the motor. Like parts have been given like references.

Gyroscope 1 is arranged as previously described and lever 4 is coupled to the rotor of synchro transmitter 7 by means of link 5 and arm 6. As previously explained, three single-phase voltages appear between output leads 19 from the three winding stator of transmitter 7.- For the purpose of the present embodiment the mechanical arrangements are such that when arm 6 is in the position corresponding to the neutral position of the ship (i.e., the ship is upright and there is no roll or heel) then the voltage between leads 19 and 19 is zero. These two leads are connected to primary winding 24 of step-up transformer 25 and two equal impedances 26 and 27 are connected between leads 19 and 19 respectively and the third lead 19 The object of the impedances is to provide approximate balance in the load on the three synchro stator windings. Secondary winding 28 of transformer 25 is connected to winding 16 of the two-phase motor. Transformer 25 is not essential but it may be used to match the synchro to winding 16 of the motor. The second stator winding 29 of the motor need not be centre-tapped for this embodiment and it is connected to the alternating current supply through capacitor 30.

voltage is applied to leads 22 of the cross winding of synchro 7 so that the axis of the field set up by the energizing winding of synchro 7 is also displaced by man bination of the field set up by the cross winding with that due to the energizing winding. This angle also corresponds to the angle of heel. Thus, although lever 6 is moved by lever 4 to a greater extent to one side of its normal central position than to the other side, the change in the axis of its rotor field corresponds to the difference so that the output signal from leads 19 is exactly the same as if no heel were present. 7

If the angle of heel changes then sector plate 11 is, over a period of time, moved to a new central position Rotor 17a of the two-phase motor 17 is connected through reduction gearing to the spindle of a synchro transmitter 20, whose rotor is energized from the alter nating current supply. The rotor of synchro 20 is the control member in this embodiment of the invention. Only one stator winding of this synchro is used and its terminals 23 are connected to terminals 22 of synchro 7. In place of synchro 20 an induction regulator orother device may be used which will provide an alternating voltage which varies with the angular position of its rotor.

In operation, rolling causes the arm 6 to be oscillated and the voltages between lines 19 are varied. When arm 6 moves in one direction from the neutral position an alternating voltage appears in winding 24 of transformer 25 and a corresponding voltage appears in winding 16 of motor 17 which runs in one direction. When arm 6 moves in the other direction the voltage in winding 16 is of opposite phase and consequently rotor 17 runs in the opposite direction.

The mechanical arrangements are such that when arm 6 is in the neutral position the winding on the rotorof synchro 20 is at right-angles to the stator winding, so

that no voltage appears across terminals 22 of synchro 7. When rotor 17:: runs for equal periods in opposite directions in response to the roll signals from gyroscope 1, the rotor of synchro 20 is only oscillated through a small angle and no appreciable voltage is applied to terminals 22. When the ship heels the rotor of magslip 20 is gradually displaced to one side or other of the neutral position according to the direction of heel; consequently a voltage appears in the stator winding of synchro 20 and is applied to terminals 22 so that the axis of the field set up by the energizing winding of synchro' 7 is displaced by vector combination with the field set up by the cross Winding. The effect is exactly the same as in the previous embodiment and the signal transmitted over leads 19 is modified in exactly the same way; consequently the voltage between leads 19 and 19 is now zero when the ship is in the mid position between the extremes of the roll and motor 17 is operated accordingly.

It will be understood that the invention may be incorporated in any form of control gear and that many modificationsmay be made in the practical embodiment of the invention without departing from its scope.

I claim:

1. In a ship stabilization control gear the combination which consists of a vertical-keeping means, means coupled to the vertical-keeping means for producing a stabilization signal proportional to the instantaneous angle of ship roll in relation to the vertical, means coupled to the vertical-keeping means for producing a second signal corresponding to the mean angle of ship roll in relation to the vertical and means for modifying the stabilization signal by the second signal to produce a modified signal proportional to the instantaneous angle of ship roll in relation to the mean angle of roll.

2. In a ship stabilizer, control gear the combination which consists of a datum member to provide a true vertical datum, a device coupled thereto to derive therefrom a first signal proportional to the instantaneous angle of roll in relation to the vertical datum, a rotatable control member, a motor, the rotor thereof mechanically coupled to rotate the control member, control means for the motor depending upon the position of the control member and operated according to the relative angular displacement between the datum member and the control member whereby the control member rotates very slowly in one direction or the other according to the instantaneous direction of angle of roll and eventually oscillates about the mean position between the extremes of the movement, means coupled to the control member to derive a second signal proportional to the angular position of the control member, means associated with said device and connected to receive the second signal and operative responsive to the second signal to modify the first signal whereby to produce a signal for operating the control gear corresponding to the instantaneous angle of roll in relation to the angular position of the control member.

3. In a ship stabilizer, control gear the combination which consists of a vertical-keeping free gyroscope, a synchro transmitter for producing a signal for operating the control gear, the rotor thereof having an energising winding and a second cross winding at right angles to the energising winding said rotor being mechanically coupled to the gyroscope to be displaced according to roll angle, a rotatable control member, a contact arm on the control member, a mechanical coupling between the gyroscope and the contact arm, a motor, the rotor thereof mechanically coupled to rotate the control member, control contacts for the motor carried on the control member and operated by the contact arm according to the relative movement between the gyroscope and the control member whereby the motor rotates the control member very slowly in one direction or the other according to the instantaneous direction of roll and eventually oscillates about the mean position between the extremes of the movement, an induction regulator, a rotor thereof mechanically coupled to the control member to provide a signal corresponding to the angular position of the control member, the output of the induction regulator being applied to the cross winding of the synchro transmitter to rotate the axis of the synchro magnetic field.

4. In a ship stabilizer, control gear the combination which consists of a vertical-keeping free gyroscope, a synchro transmitter having three stator windings and a rotor, the rotor being mechanically coupled to the gyroscope and having an energising winding and a second winding at right angles to the energizing winding to be displaced according to the roll angle, an electrical device comprising a stator and a rotor to produce a voltage dependent upon the angular position of the rotor, a motor mechanically coupled to rotate the rotor of the electrical device, a stator winding of the motor connected to two stator windings of the synchro transmitter, the synchro transmitter being so phased that when the roll angle is zero the voltage in the stator winding connected to drive the motor is zero, load balancing impedance connected from the third winding of the synchro stator to the other two windings of the synchro stator, and the output of the electric device being applied to the second winding on the rotor of the synchro transmitter to rotate the axis of the synchro magnetic field.

5. The combination as claimed in claim 4, in which a transformer is interposed between the synchro stator windings and the motor stator winding.

References Cited in the file of this patent UNITED STATES PATENTS 1,232,619 Sperry July 10, 1917 2,046,735 Frisch et al. July 7, 1936 2,492,148 Herbold Dec. 27, 1949 2,553,560 Esval May 22, 1951 2,588,213 Davis Mar. 4, 1952 2,595,250 Harcum May 6, 1952 

